A Plasma Display Panel (PDP) is a flat display element, which is mainly used for large-sized display devices over 40 inches because the PDP is thin and light and gives good image quality In the PDP, pixels are formed at points where barrier ribs and address electrodes formed on a rear plate intersect sustain electrodes formed on an front plate to realize an image.
This PDP is schematically shown in FIG. 1. Referring to FIG. 1, a dielectric layer 90 is coated on a rear plate 80 made of a glass or metal substrate, and address electrodes 50 are formed on the rear plate 80 or the dielectric layer 90. Barrier ribs 60 having a long stripe shape are positioned between the address electrodes 50, and fluorescent substances are coated on the surface between the barrier ribs 60 in order to compose a sub-pixel. A sustain electrode 40 is in an front plate 1 made of glass, and a dielectric layer 20 and an MgO protective layer 30 exist below the sustain electrode 40. Thus, when the front plate 10 is combined with the rear plate 90, there generates a plurality of pixel spaces separated by the barrier ribs 60. These separated spaces are filled with He/Xe gas or Ne/Xe gas so as to create plasma therein when voltage is applied to the sustain electrode 40 and the address electrode 50. In addition, vacuum ultra violet generated from the plasma excites the fluorescent substances coated on sides of the barrier ribs and lowermost surfaces between the barrier ribs, thereby creating red, green and blue visible light.
In order to form the barrier ribs, the sand blasting is mainly used. FIG. 2 schematically shows sequential processes of the sand blasting. As proposed in Japanese Patent Filing No. 11-120905 and Korean Patent Filing No. 2000-10322 in detail, the sand blasting is executed according to the following procedure: coating paste containing glass powder for barrier rib and a ceramic filler on a rear plate substrate such as a glass board and then drying, which is repeated several times until to have a thickness of about 200 μm; coating photoresist on the dried thick film; and developing the film except portions corresponding to the barrier ribs so that areas except the barrier ribs are removed. At this time, the exposed portion is determined according to the type of the used photoresist film. And then, ceramic powder such as calcium carbonate (CaCO3) is sprayed together with pressed air onto the film coated with photoresist in order to etch the portions where the photoresist is removed, thereby forming the barrier ribs.
This sand blasting is relatively stable and thus frequently used to make the rear plate barrier ribs of the existing PDP. However, the sand blasting has drawbacks in the facts that many and complicated processes are required to manufacture the barrier ribs, the side shapes of the manufactured barrier ribs are not uniform, and the drying and coating process is executed very slowly.
Recently, as the contrast of the PDP improves, the pitch of the sub-pixel between the barrier ribs is decreased from 420 μm to 200 μm, which needs a method for making a barrier rib having a thickness less than 50 μm. In case the pitch of the sub-pixel is 200 μm and the thickness of the barrier rib is 50 μm, the open ratio becomes 50%, while in case the cell pitch is 100 μm, the open ratio becomes 0%, and thereby is it impossible to compose the display panel. Thus, it is required that the barrier rib has a thickness between 20 μm and 30 μm. However, the sand blasting is substantially impossible to obtain such thickness. Since ceramic powder and high-pressure gas are used for etching to form the barrier ribs, it is hardly possible to make a thin barrier rib since the barrier rib is broken due to the mechanical energy of the ceramic powder and the high-pressure gas. In addition, if the pitch of the sub-pixel is 430 μm and the width of the barrier rib is 50 μm when making the barrier ribs using the sand blasting, at maximum 90% of the volume of the thick film is etched and abolished. Thus, the sand blasting generates a large amount of wastes. Furthermore, since the thick film has glass frit containing a large amount of lead monoxide, the wastes may cause environmental pollution.
As another example, a method for forming barrier ribs by etching the sintered glass (SID 01 Digest, p 537 (2001).). This method is now briefly described. At first, a thick film having a predetermined thickness is formed on a glass substrate by using the paste including glass powder and ceramic powder. The thick film may be formed by using the well-known printing and drying process repeatedly, or by lamination using a dry film (or, a green tape). If the thick film is formed, the thick film is heated up to a predetermined temperature by means of a predetermined temperature profile, and then sintered to make a thick film made of barrier rib materials. A photosensitive film is coated or laminated on the surface of the sintered thick film, and then the photosensitive film is selectively exposed by using a mask. The exposed specimen is developed to form an etching protective pattern film by means of the photosensitive film, and then the exposed thick film is etched using a suitable etching liquid. And then, through washing and drying barrier ribs for PDP are finally manufactured. This method may advantageously make a barrier rib having fine and complex figure since it does not require the etching process using mechanical impacts. However, the dense glass thick film is generally slowly etched, particularly experiencing the isotropic-etching. Thus, Photonics Co. provides a method for improving a barrier rib forming speed by etching a porous thick film (SID 01 Digest, p 532 (2001)).
Such etching method has some problems as follows.
First, since the barrier rib material layer formed by sintering is etched by an etching solution such as acid, environmental pollution may be caused by wasted water. Since the layer to be etched is thick as much as 120 μm˜150 μm, an amount of the wasted water is very significant, thereby requiring much costs for treating the wasted water.
Second, physical features required for the barrier rib material such as electric resistance, dielectric constant, thermal expansion coefficient and reflectivity should be satisfied, and the material should be rapidly etched by the water-based solution. Thus, there are many limitations in selecting the material, and thus the selection of the barrier rib material is very limited.
Third, when applied to a large area, this etching method may hardly obtain a uniform etching speed. In other words, in order to have a uniform etching speed throughout the large area and give a desired shape for the barrier rib of the PDP, the etching conditions should be maintained very accurately. However, to maintain the conditions throughout the large area is very hard, thereby resulting in very low process yield.